Traditional harvesting methods for zooplankton are based on filtration of water by means of a very finely meshed trawl. Regarding the trawl, it must be quite large in order to obtain harvest volumes of significance. A large finely meshed trawl made of flax provides a very large drag force when it is towed through the sea, thus the consumption of fuel on the trawling vessel is very high. Another disadvantage is that the trawl must be towed at a depth of 30 to 40 meters. It is also possible to use harvesting or sieving cages for the harvesting of zooplankton.
It is known techniques from particle purification of water that one may release air bubbles with particle size so that these due to the surface tension of water will attach to the particles in order for said particles to be brought to the surface for filtration or skimming.
The inventors know of whales that may delimit a school of fish by means of releasing air bubbles which scare and thus encloses the school behind a curtain formed more or less as a purse seine.
The following documents have been found to mention bubble diffusers in water:    NO 54817, “Device for leading fish, herring and the like during harvesting” (1932)    NO27776 “Method for the lifting of a mass of fish in seines, nets and the like”.    WO 9219100 (PCT/N092/00082), “Method of leading and trapping fish in the sea, and equipment for use in carrying out the method.” (1991)    DE 100 28 313 “Fischfanggerät”.
Other less relevant patent publications describe the flushing of the sea bed ahead of a trawl to take up shells, as well as built in pumps on a trawl. Pumps are relevant to a pumping device in the present application, but do not anticipate the present application. None of the above patent publications describe zooplankton being harvested. The shown bubble diffusers do not describe diffusers arranged for making fine millimeter size bubbles which shall attach to the zooplankton by means of the surface tension of water. The above mentioned patent publications do not describe the bubbles pacifying the organisms, but rather that they are either scared upwards, or entrained by an overwhelming amount of upwardly flowing air bubbles, thus a much more coarse mechanism than the one which is used in the present application.